Soil PhysicoChemical Classification (nfm)

group

grain size

composition

Name

Factors influencing Magnitude & Rate of Volume of Change

sedimen -tary

clastic

appreciable quantity of grains more than 2 mm diameter

rounded pebbles in medium graines matrix

conglomerate

Factor

Description

angular coarse rock fragments, often quite variable

Breccia

Composition of solids

A high percentage of active clay minerals include montmorillonites and miwed layer combination or it and other clay minerals that promote volume change

more than 50% of grains are 0.06 - 2 mm diameters

Medium quartz grain

less than 10% of other minerals

siliceous sandstone

appreciable quantity of clay minerals

argillaceous sandstone

appreciable quantity of calcite

calcareous sandstone

Concentration of pore fluid

high concentration cations in the pore fluid tend to reduce the magnitude of volume change: swell from osmosis can be significant over long periods of time

appreciable quantity of iron oxide cement

ferruginous sandstone

over 25% felspar, less than 75% quartz

arkose

Composition of pore fluid

Prevalence of monovalent cations increase shrink-swell, divalent & trivalent cations inhibit shrink-swell

10-50% felspar and darker minerals, 30 - 60% quartz

gravvache

> 50% of grains 0.002 - 0.05 mm diameter

fine to very fine grains with clays minerals

siltstone (if laminated claystone

Dry density

high initial dry densities result in closer particles spacing and larger swells

predominantly grains less than 0.002 mm diameter

microscopic clay minerals

less than 10% other minerales

shale if net laminated claystome

appreciable calcite

calcareous shale

Structure

flocculated particles tend to swell more than dispersed particles, cemented particles tend to reduce swell, fabrics that slake readily may promote swell

appreciable carbonaceous material

carbonaceous shale

appreciable iron oxide cement

ferruginous shale

Ground water

fluctuating and shallow water table (less than 6m from ground surface) provide a source of moisture for heave

organic

variable

calcite and fossils

ferruginous shale

carbonaceous material

fossiliferrous limestone

Drainage

poor surface drainage leads to moisture accumulation or ponding

chemi cal

microscopic

calcite

limestone

dolomite

dolomite

Field permeability

fissures significantly increase permeability and promote faster rates of swell

Quartz

chert, flint, etc.

Iron compounds with quartz

Iron

Vegetative cover

trees, shrubs & grasses are conducive to moisture depletion by transpiration, moisture tends to accumulate beneath areas denuded of vegetation

Halite

rock salt

gypsum

rock gypsum

meta- morphic rocks

Folia -tion

coarse crystalline & banded

coarse crystalline

medium crystalline

fine to microscopic crystalline

Confinement

Larger confining pressures reduce swell: cut areas are more likely to swell than filled areas; lateral pressure may not equal vertical overburden pressures

foliated

gneiss

schist:talc, chlorite, hematite, etc.

phyllite

slate

non foliated

marble, quartzite, serpentine, scapstone

marble, quartzite, serpentine, scapstone

mornfels, anthracite coal, marble, quartzite, serpentine, scapstone

Soil Hydrology and Weathering

Description of Typical Weathering Profile

Swell potential ad Atterberg Limits

Zone

Description

RQD (NX core percent)

% core recovery (NX core)

Reltive permeability

Relative strength

index property

Swelling potential

I Residual soil

1A - A horizon

top soil, roots, organic material zone of leaching & elluviation may be porous

-

0

medium to high

low to medium

low

Medium

High

1B - B horizon

- clay enriched, accumulation of Fe, Al, Si, may be cemented, no relict structures present

-

0

low

low but high if cemented

liquid limit

30 - 40

40 - 55

55 - 90

1C - C horizon

- relick rock, silty grading to sandy material - <10% core stones, often micaceous

0 or not applicable

generally 0 - 10%

medium

low to medium (relict structures significant)

plastic limit

15 - 20

20 - 30

30 - 60

II Weathered

IIA transition: from residual or saprolite to partly weathered rock

- highly variable, soil or rock like - fines to coarse sand - 10 - 90% core stones - spheroidal weathering common

variable, generally 0 - 50%

variable generally 10 - 90%

high (water losses common)

medium to low

where waste and relict structures are present

shrinkage liimit

35 - 25

25 - 14

14 - 8

IIB partly weathered rock

- rock like, soft to hard, - joints stained to altered - somme alteration of feldspars & micas

generally 50 - 75%

generally > 90%

medium to high

medium to high

free swell

20 - 40

40 - 70

70 - 180

unweathered rock

- no iron stains to trace

long joints - no weathering of feld- & micas

> 75% gene-rally >90%

generally 100%

low to medium

very high